Articulated multi-unit rail road cars typically have at least two railcar units permanently joined to each other end-to-end at an articulation connection. Most commonly, the adjoining railcar units share a truck, with the articulated connector being mounted over the truck center. In a conventional three-unit articulated rail road car, an intermediate, or middle railcar unit, may typically share a truck with each end railcar unit. The ends of the intermediate railcar unit are joined to the respective adjacent ends of the end railcar units by articulated connectors. A typical articulated connector includes a female articulated connector portion, or socket, mounted to one railcar unit; and an opposing mating male articulated connector portion, or member, mounted to the next adjacent railcar unit. Conventionally, the intermediate railcar unit in a three-unit rail road car is provided with an asymmetric arrangement of articulated connector portions, that is, it has a female articulated connector portion at one end and a male articulated connector portion at the opposite end. Correspondingly, the end railcar units have counterpart male or female articulated connector portions, as the case may be. In that style of layout, all female articulated connector portions extend toward the same end of the three-unit rail road car.
In order to control “side sway”, or roll, of one railcar unit relative to the next adjacent railcar unit, at each end having an articulated connector each railcar unit has a pair of side-bearing support arms. In one arrangement, at one end of the intermediate railcar unit, a narrow pair of side-bearing arms is nested within an opposing, relatively wider pair of side-bearing arms mounted to the adjacent end railcar unit. The side-bearing arrangement is reversed at the other end of the intermediate railcar unit such that the latter is provided with the wide pair of side-bearing arms and the adjacent end railcar unit has the narrow pair of side-bearing arms.
The ride characteristics in a conventional three-unit rail road car may tend to vary depending on the direction of travel. More specifically, it appears that the car may tend to perform “better” in one direction of travel than in the other, particularly when the car is running over curved portions of track. It has further been noted that the wheels of the shared trucks may tend to be subject to greater lateral forces when the car is travelling in the direction associated with less satisfactory performance. It is thought that in addition to causing uneven wear on the truck wheels, this may also tend to increase the likelihood that the wheels will ride up on the rail, and jump the track.
The propensity of the wheels to ride up on the rail may be considered to be a function of the L/V ratio, where L is the lateral force to which the truck wheels are subject and V is the vertical force carried by the truck wheels. The higher the L/V value, the greater may be the likelihood that the truck wheels may tend to ride against the rail when the car negotiates a curve in the track. Accordingly, lower L/V values for the truck wheels may tend generally to be desirable. However, in a conventional rail road car of the type described above, under certain circumstances, the L/V values for the truck wheels may be significantly greater in one direction than the other. This may tend adversely to affect the stability of the car and may tend to generate undesirable vibration throughout the car structure. This in turn may ultimately lead to crack propagation and failure in the car, and consequently to costly car maintenance and repair. In addition, when travelling over a curved portion of track, the side-bearing arms in some of these cars may be subject to undesirably high forces further encouraging vibration in the car structure.
The difference in dynamic performance of the rail road cars may tend to be more (or less) pronounced depending on variation of the frequency of the input perturbances. That is, performance may tend to be a function of frequency and evaluation of the various alternatives may require optimization over the full range of forcing frequencies associated with in-service operation. It has been noted above that dynamic performance may be “better” in one direction than another. The term “better” needs to be understood in the expected operational life. An arrangement that may provide very good performance at one frequency, may provide very poor performance at another, such that, overall, it may be inferior to another layout that produces moderately good performance across the spectrum. In that context, the assessment of “better”, is an overall evaluation performance.
The disadvantages associated with the conventional asymmetric three-unit articulated connector and side bearing arm arrangements noted above may not be restricted to three-unit cars. Other multi-unit articulated rail road cars having a larger number of rail car units may also tend to demonstrate similar dynamic performance phenomena.
Accordingly, in the view of the present inventors, it may be advantageous to construct a multi-unit articulated railroad car having a tendency to exhibit similar ride performance characteristics in both travel directions. Such a car may tend to be less prone to the development of fatigue cracks and may have an extended service life. It would also be desirable to have a multi-unit articulated railroad car in which the forces in the side-bearing arms are reduced to yield improved ride stability of the railroad car.
In a conventional multi-unit articulated rail road car, a number of different sub-assemblies are required to construct any given unit of the car. Manufacturing may be facilitated and made more cost-effective if the number of different sub-assemblies used in a given unit were reduced.